Telescoping booms are typically used in various material handling applications by reason of increased versatility. Booms of this type include tubular sections and are commonly found on mobile cranes and forklifts. All such telescoping booms necessarily include some type of sliding and/or rolling contact between adjacent boom sections to react the loads and yet allow for telescopic movement without undue wear or friction.
Various sliding shoe or wear pad arrangements have been provided heretofore for this purpose. For example, U.S. Pat. No. 3,796,016 to Wu shows a boom with telescoping tubular sections supported by bearing plates spanning the outside corners of the inner section. U.S. Pat. No. 4,004,695 to Bickersmith shows a telescopic crane boom with separate fixed wear pads between the top, bottom and sides of adjacent boom sections. German Pat. DE No. 3101017 shows another tubular boom section supported at its rounded lower corners by contoured fixed pads. The support pad arrangements of the prior art are mainly intended to provide for sliding contact, functioning to transfer loads between adjacent boom sections by compression. However, as adjacent boom sections extend, the loading on the wear pads, particularly those engaging the lower surface of the inner boom section, increases such that engagment there approaches a point contact, which in turn results in high bending stress. Therefore, because of limitations in their wear pad arrangements, these boom sections have had to be of relatively thick-walled construction in order to handle the necessary loads. This in turn has adversely affected performance of the crane by decreasing its maximum effective reach and load capacity. Heretofore, there has not been available a wear pad arrangement that addresses the stress factors effectively.
A need has thus arisen for an improved load bearing wear pad assembly which not only meets the requirements of minimum friction and drag, but also functions to transfer loads between overlapping ends of the boom sections more efficiently so that lighter boom sections can be used without compromising the effective reach or loading capacity of the crane.